One of the questions I am most commonly asked as a psychiatrist specializing in child psychiatry is, "What causes autism?" The dissatisfying, but truthful answer is that nobody really knows. It is probably due to a variety of factors, including genetic and environmental influences. My answer, however, often leaves the questioner feeling a little bit shortchanged, especially with the current surge of new reports linking yet another "risk factor" to autism. In the last couple of months alone, air pollution, gluten sensitivity, maternal antibodies, a lack of folic acid and a number of genetic mutations have all emerged as possible causes of this spectrum disorder. Hence the question arises: why is it so difficult for doctors and scientists to pinpoint the cause for this growing and serious condition?

Perhaps a better way for me to answer this question is by clarifying that, first of all, we must appreciate that there is no "typical" autistic person. The diagnosis of ASD encompasses an enormous and diverse group of individuals with many different combinations of symptoms and a range of functional severity. This has some doctors now saying, "When you have seen one person with autism, you have seen one person with autism." It also helps to explain why the term autism spectrum disorder (ASD) has come to be a better way of speaking about this condition.

We have no definitive laboratory test or brain scans for ASD. Some new technologies, however, are being developed through research studies to help identify the condition earlier (see below). But in clinical practice, the diagnosis of ASD continues to be based on how a child behaves, as well as what can be observed about how he thinks, relates, communicates and responds. How a child behaves derives from many different causes. Instead of thinking about a child with autism who cannot talk, imagine for a moment, a child who cannot walk. There may be many reasons why that child is unable to walk -- some are very apparent, some are more difficult to determine. He or she may have a painful toe, a fractured ankle, an infection, a strained muscle or a problem with the nervous system. If we diagnose that child only on the basis of behavior (namely that the child is unable to walk), we may only be left with a diagnosis of "immobility spectrum disorder." Understanding immobility is a lot easier than understanding ASD, which is a "brain disorder." There are only several dozen joints and muscles in a human leg, and the nerves serving the muscular system are far less complex than the 100 billion neurons, and trillions of nerve connections (synapses) in the brain.

We are left, therefore, with perhaps countless different alterations in brain chemistry or anatomy, environmental exposures or genetic disturbances that could lead to the development of ASD, all with their detrimental effects on social communication, language and behavior. Autism as a spectrum, is likely a family of "autisms." Perhaps then, we should not be surprised when we hear about yet another new study suggesting a new link or a new basis for this condition.

This challenge is not unique. We continue to diagnose many other brain disorders, such as attention deficit hyperactivity disorder (ADHD), major depression, bipolar disorder and almost every other mental disorder primarily on the basis of the clinical assessment -- the patient's history, what is observed by the family, the patient himself (for older and more communicative youth and adults), teachers and other reliable sources, as well as the examination of the patient. To make matters even more complicated, there are other conditions that regularly co-exist with ASD, including ADHD, which is thought to be present in a third of children with autism.

While there is good evidence that ASD has a strong genetic component, scientists have also stressed that the increasing rates of autism cannot be explained solely by genetic changes, as our genetics are simply not changing that rapidly. So far, large-scale genetic studies are only able to explain only about 20 percent of ASD cases. We know, too, that there does not seem to be any single gene responsible. In fact, there may well be hundreds of genes interacting to cause ASD. Autism genetic research is increasingly relying on experts in computing and statistics to be able to separate out and decipher the "signal" from the "noise," to find out what is actually of significance in large genetic studies.

There are grounds for being optimistic about the future of understanding conditions such as ASD and ADHD. Researchers are developing specialized eye-tracking technologies aimed at diagnosing ASD earlier than ever before (and early detection and intervention are crucial to long-term functioning in youth affected by this condition). By detecting subtle changes in eye gaze, researchers have been able to identify ASD in children as young as 18 months of age. These eye tracking technologies, however, remain experimental and are not currently in routine clinical use. However, the FDA has just approved the Neuropsychiatric EEG-Based Assessment Aid (NEBA) system as an aid to making a diagnosis of ADHD. The NEBA system is a medical device that measures different types of brain waves, and has been shown to enhance the accuracy of an ADHD diagnosis -- when combined with a clinical assessment. Hopefully, we will see similar technologies being approved for diagnosing ASD in the future. Such advances could also allow us to develop more specialized interventions for the varied types of "autisms."

But until doctors and other health professionals are able to establish what causes ASD and tailor even better individual treatment plans than we have today, I will still have to respond to the question about what causes autism by saying that we are still trying to identify the answer. What we do know is that early identification, followed by the helpful therapeutic and educational interventions we have today, can make a world of difference for children with this all-too-common condition -- and their caregivers.